Hansen Manufacturing Corp. Of Sioux Falls, S.Dak., makes and sells enclosed belt conveyors under the trademark HI ROLLER.TM., in which the belt and the elements that support it are completely enclosed in a housing, which is usually called the "trunking." The trunking provides a structural support for troughing idlers, the belt and the material being conveyed, protects the material being conveyed by keeping out foreign substances and, in an outside installation, rain and snow, and keeps dust and any fugitive material that falls from the belt from entering the environment. The previously known HI ROLLER.TM. conveyors, which are in widespread use for conveying various materials, especially grains, have troughing idlers that resemble spools in that they have a body having a circular cylindrical medial surface and frusto-conical side surfaces that diverge outwardly from the medial surface. The belt nests in the body, which shapes the belt (in cross section) into a trough. The body is affixed to a shaft, the ends of which pass through holes in the side walls of the conveyor trunking and are supported in bearings located outside of the trunking. An important advantage of the spool-like troughing idlers is that the bearings are located outside of the enclosure and are, therefore, not exposed to any dust produced by the materials being conveyed and are accessible for greasing from time to time. Also, the likelihood of any grease that might leak from a bearing entering the trunking and contaminating the material being conveyed is very small. Inasmuch as the body and shaft rotate, dust cannot build up on them, and there are no internal fixed frames or supporting elements for the spool-like idlers within the troughing where dust can accumulate. Should a bearing fail and overheat, it is not likely to be a source of ignition for a fire or detonation of the dusty atmosphere within the troughing by virtue of its isolation outside of the troughing.
Spool-like troughing idlers have the disadvantage of inherently producing slippage between the belt and the frusto-conical side surfaces of the body, which run at a surface speed that progressively increases as a function of the distance radially from the circular cylindrical medial portion. The slippage causes wear of the belt and the side surfaces of the idler, especially if the material being conveyed includes hard, abrasive particles that can stick to the belt.
There are many specific forms of troughing idlers in which both a medial horizontal roller and separate sloping side rollers run at the same surface speeds, the rollers being of the same diameters and being mounted for rotation on separate shafts. In most designs, the rollers are tubular and supported by bearings within them that are carried by stationary shafts that are attached at opposite ends of the rollers to framing or stands. The shafts and frames are prone to buildups of dust. The bearings are close to the dusty environment of the belt, and if they fail and become highly heated, can ignite a fire. The foregoing shortcomings of previously known designs of three-roller type troughing idlers make them only marginally useful, at best, in enclosed belt conveyors, particularly for conveyors used for conveying grain where the environment is very dusty, the dust is highly flammable, and contamination is unacceptable.